Materialize safe inline SVG assets

[chubes4]

Summary

• Materialize safe accessible inline SVGs as generated SVG assets instead of serialized data URIs.
• Propagate generated inline SVG assets into artifact materialization plans for entry and non-entry pages.
• Keep decorative/unsafe SVG behavior bounded and covered by existing diagnostics.

Testing

• php -l src/HtmlToBlocks/HtmlTransformer.php
• php -l src/ArtifactCompiler/ArtifactCompiler.php
• php -l tests/contract/run.php
• cd php-transformer && composer test
• git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): openai/gpt-5.5 via OpenCode
• Used for: Drafted implementation and tests for generic Blocks Engine SVG parity; Chris reviews and owns the change.